BADSECT(8) System Manager's Manual BADSECT(8)
badsect - create files to contain bad sectors
/sbin/badsect sector ...
Badsect makes a file to contain a bad sector. Normally, bad sectors are made inaccessible by the standard formatter, which provides a for-
warding table for bad sectors to the driver; see bad144(8) for details. If a driver supports the bad blocking standard it is much prefer-
able to use that method to isolate bad blocks, since the bad block forwarding makes the pack appear perfect, and such packs can then be
copied with dd(1). The technique used by this program is also less general than bad block forwarding, as badsect can't make amends for bad
blocks in the i-list of file systems or in swap areas.
Adding a sector which is suddenly bad to the bad sector table currently requires the running of the standard DEC formatter, as UNIX does
not supply formatters. Thus to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard badsect
may be used to good effect.
Badsect is used on a quiet file system in the following way: First mount the file system, and change to its root directory. Make a direc-
tory BAD there and change into it. Run badsect giving as argument all the bad sectors you wish to add. (The sector numbers should be
given as physical disk sectors relative to the beginning of the file system, exactly as the system reports the sector numbers in its con-
sole error messages.) Then change back to the root directory, unmount the file system and run fsck(8) on the file system. The bad sectors
should show up in two files or in the bad sector files and the free list. Have fsck remove files containing the offending bad sectors, but
do not have it remove the BAD/nnnnn files. This will leave the bad sectors in only the BAD files.
Badsect works by giving the specified sector numbers in a mknod(2) system call (after taking into account the filesystem's block size),
creating a regular file whose first block address is the block containing bad sector and whose name is the bad sector number. The file has
0 length, but the check programs will still consider it to contain the block containing the sector. This has the pleasant effect that the
sector is completely inaccessible to the containing file system since it is not available by accessing the file.
mknod(2), bad144(8), fsck(8)
If both sectors which comprise a (1024 byte) disk block are bad, you should specify only one of them to badsect, as the blocks in the bad
sector files actually cover both (bad) disk sectors.
On the PDP-11, only sector number less than 131072 may be specified on 1024-byte block filesystems, 65536 on 512-byte block filesystems.
This is because only a short int is passed to the system from mknod.
3rd Berkeley Distribution BADSECT(8)